Cardio for Muscle Growth

by DeanMcKillop 4552 views Gain Muscle

Cardio for Muscle Growth

WHHHHHHHAAAAAAATTTTT? Cardio for muscle gains you say? Well, why not? All around the world, we have top tier athletes in cardiorespiratory-based sports with tremendous amounts of muscle that can perform with peak power, strength and speed. So why can't you?

Ok so maybe we can't all be elite level athletes, but we can most certainly look at some of their training approaches and apply them to ourselves. Just because the bodybuilding world may have fear mongering ‘coaches’ promoting cardio as a catabolic exercise with no benefits to muscle growth, does not mean it is correct.

In fact, it’s quite ignorant to completely remove an exercise modality without considering the context of which it can be implemented and also the proposed benefits and the proposed negatives it may have when deciding whether or not it provides a net gain or a net loss of results in your program.

So what does cardio do for us physiologically?


Cardio will increase

  • our aerobic capacity
  • circulatory oxygen utilisation
  • mitochondrial density
  • lactic threshold
  • motor unit activation
  • cardiac output (stroke volume + heart rate)
  • energy production efficiency

As you can see, cardiorespiratory training has a multitude of physiological benefits, of which all provide benefits for weight training as well. But before I go further with my application advice, it’s important to understand the differences in cardio modalities as well, as not all are created equal.

Cardiorespiratory training can be broken down into two categories:

1 – Anaerobic

Exercise completed at either a submaximal or maximal intensity for short bursts in time, at or above the lactate threshold without the presence of oxygen required for energy production.

2 – Aerobic

Exercise completed at a submaximal intensity for a longer duration, below the lactate threshold and with the presence of oxygen being required to produce energy.

Think of your anaerobic system as your power providing system and your aerobic as your sustainable energy providing system. As you can begin to postulate, both aerobic and anaerobic training have benefits for weight training performance and therefore can also enhance your ability to grow muscle indirectly.

The question is though, how much is too much cardio and what cardio is best for strength based athletes versus someone just looking to enhance their physique?

Well here are the top 3 factors to consider:

  • Effect on recovery - If we do too much cardio will it reduce our weight training performance
  • Effect on muscle mass - Will too much low-intensity steady state (LISS) cardio enhance the risk of muscle loss. Likewise, will high intensity interval training (HIIT) enhance the risk of muscle loss
  • Effect on hormonal output - Does cardio negatively impact metabolism and if so how much is too much

Contrary to popular belief, cardio is not actually a negative modality of exercise when it comes to muscle retention or growth. Sure if it was the primary modality of exercise and no resistance training was being utilised there may be some negative effects on lean body mass (LBM), however for the purpose of the remainder of this paper, I will be assuming cardio in this instance is a supportive secondary modality and not a primary one.

Within this context, resistance training and strength maintenance/progression is going to be the primary determinant alongside dietary intake that is responsible for controlling the amount of muscle you can retain in a calorie deficit or gain in a calorie surplus.

It has previously been proposed that cardio may lead to an increase in muscle wastage and a reduction in metabolic capacity may occur. However, according to the most recent research, this is just not the case.  While some studies have shown reduced thyroid output during exercise studies (1,2), the determining factor for this response was in fact due to calorie restriction and not the exercise itself (1).

Similarly, in well-trained endurance athletes who were given oral T3 hormone, showed elevated levels of circulating thyroid hormone regardless of the amount of exercise they participated in (3). In essence, this shows that exercise itself and more specifically endurance exercise does not have negative implications for thyroid but more so the stats of calorie intake does.

It may be worth considering the context of this information, however, as a combination of both excessive amounts of cardio and calorie restriction may enhance the negative maladaptations of your metabolic capacity during caloric restriction.

Furthermore in studies looking at the effects of exercise intensity on circulatory thyroid hormones, it has been found that high-intensity exercise results in a greater post workout suppression of T3 (2), which is worth consideration when looking at the recovery of hormone status in a calorie deficit for natural athletes. However in long term studies not looking at the acute effect but instead the effects of exercise over time, no direct down-regulation as a result of exercise was noted (4, 5), but instead, changes in body composition and dietary intake were more closely related to thyroid hormone status once again (5).

people running

In conclusion, the current fear of cardio-respiratory training and its effect on metabolic hormone status is one that cannot currently be supported undeniably by science. Current research indicates that calorie deficit status and body composition are in fact the primary determinants of metabolic health (6), of which exercise does not appear to enhance its effects as a direct relationship to the exercise type and intensity at this stage. 9

As it stands, the benefits of cardio-respiratory training on health markers and performance enhancement far outweigh the unfounded concerns of the fear mongering cardio society. It is my opinion, that cardio should be used as a supportive measure to enhance total body health and performance, which in turn will allow for a greater output in resistance training and therefore elicit greater muscle growth and power output. Which is especially the case in athletes not utilising any higher oxygen debt-inducing exercise such as high reps, intervals, sled work or intensity techniques.

Final Notes

Cardiorespiratory exercise of both LISS and HIIT can be utilised effectively to maximise mitochondrial health, provide more oxygen to the blood, improve work capacity and enhance muscular recovery from metabolic waste accumulated during exercise.

Cardio is not the one to blame for muscle loss but instead when used inappropriately in the context of a severe caloric deficit in the absence of strength maintenance or progression, may enhance the negative adaptations to a poor environment in its entirety.

For a strength or body composition dominant athletes, the primary concern should always be for performance enhancement or maintenance in their chosen modality of sport and cardiorespiratory training should only ever be used as an accessory.

While cardio is not a necessity, it absolutely can offer benefits to the strength athlete. 

Loucks, A.B., Callister, R. (1993). Induction and prevention of low T3 syndrome in exercising women. The American Journal of Physiology. 264(2). Pp 924-930.

Anthony, C. et al. (2012). Thyroid hormonal responses to intensive interval versus steady state endurance exercise sessions. Hormones. 11(1). Pp 54-60.

Rone, J.K., Dons, R.F., Reed, H.L. (1992). The effect of endurance training on serum triidothyronine kinetics in man: physical conditioning marked by enhanced thyroid hormone metabolism. Clinical Endocrinology. 37(4). Pp 325-330.

Wesche, M.F., Wiersinga, W.M. (2001). Relation between lean body mass and thyroid volume in competition rowers before and during intensive physical training. Hormone and Metabolic Research. 33(7). Pp 423-427.

Tremblay, A. et al (1997). Endurance training with constant energy intake in identicl twins: changes over time in energy expenditure and related hormones. Metabolism: Clinical and Experimental. 46(5). Pp 499-503.



Exercise Scientist

I completed my Exercise Science Degree at the University of QLD and have worked in the fitness industry for over 8 years, including a short stint at the Brisbane Broncos in 2010 as a student. I also hold my Level 2 Strength and Conditioning Coach accreditation (ASCA) and have competed in 1 bodybuilding season, placing 2nd at the IFBB u85kg Nationals.

ViewDean's Articles